The commonest benign neoplasms are hamartoma, leiomyoma, neurogenic tumour and lipoma. They are usually well demarcated, round and less than 2 cm in diameter, with typical radiological appearances of a smoothly marginated intraluminal polyp. Hamartomas and lipomas may demonstrate fat attenuation on CT.

Tracheobronchial papillomatosis is a particular entity caused by human papillomavirus infection usually acquired at birth from an infected mother. The larynx is affected most commonly; extension into the trachea and proximal bronchi occurs occasionally. Exceptionally, the infection spreads into the lung parenchyma. The typical radiological findings consist of multiple small nodules projecting into the airway lumen or diffuse nodular thickening of the airway wall. Although benign, papilloma may undergo transformation to squamous cell carcinoma.

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